In Antigone, how might the impact of Antigone's choice on others be compared to that of Helen of Troy in Homer's Iliad?
This is an interesting question to consider. Antigone is a character who is so determined to act in burying her brother in opposition to Creon's decree that she does not even consider the possible consequences that her act might have on those around her, in particular her sister and Haemon, the man she is going to marry. Her actions and her motivation are all about pleasing the dead more than the living. Note what she says in the following quote:
And even if I die in the act, that death will be a glory.
I will lie with the one I love and loved by him--
an outrage sacred to the gods! I have longer
to please the dead than please the living here.
In a sense, Antigone's single-minded focus on this "outrage" and her determination to see her brother properly buried leads her to act in a way that places those around her in a very difficult and dangerous position, as demonstrated by the fate of those nearest and dearest to her. She chooses to act in a way that ignores or is blind to how that choice will impact others, and cause them great suffering.
In Homer's Iliad, by contrast, Helen of Troy is a character who does not seem to have actually been allowed to make a "choice" of her own free will. Homer is very ambiguous as to whether she goes with Paris out of free will or whether she is going with him thanks to Aphrodite's arts. Although her act of going to Troy clearly has massive ramifications, as it starts the Trojan War, at the same time Homer suggests that it is problematic to blame Helen herself for this, as her journey to Troy has as much to do with Paris and Aphrodite as her own free agency. Note the way she seems perfectly happy to return to her original husband, Menelaus, after the end of the war.